1. Field of the Invention
This invention relates to devices for hydraulically expanding plastically deformable conduits, and in particular to an improved fluid mandrel having an eddy current probe assembly for precisely locating the mandrel in a desired section of the conduit.
2. Description of the Prior Art
Fluid mandrels for hydraulically expanding plastically deformable conduits are known in the prior art. Such mandrels, working in conjunction with hydraulic expansion units, are frequently used to perform maintenance on the heat exchange tubes of a nuclear steam generator. For example, such mandrels may be used to join a reinforcing sleeve to the inside walls of a heat exchange tube which has been damaged by corrosion or by mechanical shock. In such applications, the reinforcing sleeve is first functionally engaged over head of the the fluid mandrel, and the combination of this sleeve and mandrel is slid into the mouth of the heat exchange tube to be repaired. The head of the mandrel, which generally includes a configuration of sliding O-rings and an orifice which discharges hydraulic fluid at high pressure, exposes the inside of an axial section of the sleeve to a high hydraulic pressure. This pressure, in turn, elastically and then plastically expands the section of the sleeve into the walls of the tube, which ultimately causes the tube to expand plastically with the sleeve. The end result is that an interference joint is created between the tube and the reinforcing sleeve.
One of the most serious drawbacks of prior art fluid mandrels is that they include no provision for accurately locating the mandrel within a desired axial section of the tube. More specifically, if the maintenance operator wishes to perform an expansion on one of the heat exchanger tubes in a precise location, such as the section of the tube which is surrounded by the bore of a baffle plate, he must first locate this section of the tube by means of a separate eddy current probe before inserting the fluid mandrel up into the desired section of the tube. He must then carefully slide the fluid mandrel to the exact location indicated by the eddy current probe, taking into account inaccuracies caused by the axial compression of the high pressure hose which occurs when the mandrel is forcefully slid up the tube. Such a two-step process of locating the area of the tube desired to be expanded is not only awkward, time-consuming and sometimes inaccurate.
Clearly, a need exists for an improved fluid mandrel which includes an eddy current probe assembly which eliminates the awkward and dangerous two-step process of properly locating the fluid mandrel inside the tube. Ideally, such a probe should be detachably mountable onto conventional fluid mandrels.